Get your design, letters or paths ready and ensure that you have Stroke selected in the Tools palette, rather than Fill. Then open the Swatches palette.
Click on the orange-yellow gradient then increase the Stroke width to 30pt. Click on the Gradient palette to see the default of applying gradient within stroke.
Drag the yellow gradient control to the middle then Option/Alt-drag the red one past it to the left. Now select Apply gradient across the stroke.